In construction, reinforcing steel may be supplied in a variety of different forms. Typically the reinforcing steel is known as rebar and is available in a variety of diameters and textures. The most common texture is that of a double helical raised spiral surface, which forms a pair of opposite spiral patterns as viewed from one end of the rebar to the other. The raised spiral surfaces enable the rebar to engage the concrete commonly known as deformed bar or rebar. In instances where the rebar may be either built together or inserted into cement, the rebar extends straight up from the cement surface of the freshly dried concrete.
The necessity for not pre-bending the rebar must not be overlooked. Even where the rebar is pre-bent for the purpose of forming advantageous shapes to reinforce the concrete, the ends will need to be left straight until after pouring, since the level of the concrete may vary depending on the accuracy of the pour. The shape and extent of the rebar which exists after the concrete form is made is important to the structural integrity of the other concrete forms which will be combined with the rebar which is to be bent for proper clearance.
Further, the structural integrity of the exposed rebar itself can be critical to the further structures which are formed with and integral to the rebar which is bent. Where the rebar is attempted to be bent without further aid, a corner bend is made at the surface of the cement. This is especially harmful, and can virtually eliminate the usefulness of the exposed rebar. In the best case, the rebar can simply break off. At least a complete failure will form an overt indication that there is no rebar to use. A complete failure may cause the complete re-pouring of the structure, but at least it will not lead to the reliance on the damaged structure and therefore result in a later failure and possible loss of lives.
Other methods may involve the manual bending of the rebar around an object placed adjacent the area of the rebar extending into the concrete. The problems with this method are many. In some cases the object will move causing the bulk of the bending moment to occur at the concrete surface, with only a gently sloping bending applied to the remainder of the rebar. In this case, the construction inspector may be fooled into believing that the rebar is properly bent, when in fact the structural damage done is equivalent to that for a straight angle bend.
Further, the size of the rebar can cause a different result for different objects. The radius of the bend needs to be related to the size of the rebar. A one inch diameter rebar should not be bent about a one half inch radius, and conversely, a one quarter inch rebar should not be bent about a 10 inch radius. The bend is also meant to terminate the rebar, such that tensile force parallel to the rebar as it extends from the concrete will not wholly be translated into an axial force with respect to the rebar which extends from the concrete. A sharper bend is associated with the creation of force against the bend, whereas a shallow bend enables the rebar to exert more of an axial pulling force in the concrete into which it is placed.
It is for these reasons that a gentle and well placed bend is so important to enable the resulting structure to maximally take advantage of the full strength available in the rebar, as well as the holding force of the rebar which extends parallel to and along the surface of the concrete from which it extends. One result of the need for well placement is the need to have an even radiused bend occur at varying heights above the surface of the concrete. Where an object is used to assist the bending of the rebar, it will usually not have the stability to enable the bend to occur at various heights. Where the person bending the rebar is using force about an object, the object must be of the correct radius and have an adequate height.
Such an object would be prohibitive to be placed between extending lengths of rebar particularly where the spacing is narrow, such as between about one foot and about six inches. Further, workers may not be expected to physically transport such a device, and may require the help of a crane. Even where a structure for rebar bending is employed, the construction worker must still effect the bending. Typically this is done with mechanical advantage by the use of a pipe placed over the end of the rebar, combined with tugging and pulling on the pipe. Even where a properly diameter structure is present, such haphazard bending is problematic, for a number of reasons.
First, the bend may still not be proper. Second, the time for physical manipulation is prohibitive. Third, the bending may "trap" the device or die about which the rebar is bent. The time consumed for a single worker to bend each rebar set, which is prohibitive, will be even worse if manual bending results in a trap of the structure. A trapped structure can cause the worker to have to bend the bar back to free the structure. Bending the rebar both ways significantly weakens the rebar.
What is therefore needed, in the construction field, is a device and method for enabling the quick, safe, easy and sure bending of rebar. The needed device should have a number of characteristics which give it utilitarian advantages on the job. The characteristics should include the inability of the device to become "trapped". The bending should be able to be achieved at varying heights above the level of the concrete surface. The bending should always produce an even radius of curvature. The bending should be automatic to eliminate the energy expenditure by the construction worker. The device used for bending should be portable and as light weight as possible to facilitate its use between closely set rebar and also at elevations significantly above ground level.